A putative helical domain in the MalK subunit of the ATP-binding-cassette transport system for maltose of Salmonella typhimurium (MalFGK2) is crucial for interaction with MalF and MalG. A study using the LacK protein of Agrobacterium radiobacter as a tool
Abstract
The ATP-binding-cassette (ABC) protein LacK of Agrobacterium radiobacter displays high sequence similarity to the MalK subunit of the Salmonella typhimurium maltose-transport system (MalFGK2). We have used LacK as a tool to identify sites of interaction of MalK with the membrane-integral components MalF and MalG. Small amounts of LacK, resulting from the expression of the plasmid-borne lacK gene, proved to be sufficient for partial restoration of growth of a malK strain of S. typhimurium on maltose. LacK failed to substitute for MalK in regulating the expression of maltose-inducible genes but the hybrid complex MalFGLacK2 was sensitive to inducer exclusion. The lacK gene also complemented a ugpC mutant of Escherichia coli to growth on sn-glycerol-3-phosphate as the phosphate source. Partially purified LacK exhibited a spontaneous ATPase activity comparable to that of MalK. A MalK"-'LacK chimeric protein was isolated (by in vivo recombination) in which the N-terminal 140 amino acids of MalK are fused to residues 141-363 of LacK. The protein substituted for MalK in maltose transport considerably better than LacK. Furthermore, random mutagenesis of the plasmid-borne lacK gene yielded three clones that were superior to wild-type la...Continue Reading
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